Interfacial Ising Superconductivity Emerges in Trilayer Gallium, Achieving 21.98T Critical Fields at 400 mK

Superconductivity, the ability of a material to conduct electricity with zero resistance, continues to surprise scientists with its diverse forms, and recent research explores how confining ultra-thin layers of materials can unlock novel superconducting behaviours. Hemian Yi, Yunzhe Liu, Chengye Dong, and colleagues demonstrate a particularly robust form of superconductivity in a carefully constructed layer of gallium, sandwiched between a silicon carbide substrate and a protective carbon buffer layer. The team’s work reveals that this confined gallium exhibits a unique “Ising-type” superconductivity, driven by the interaction between the gallium atoms and the underlying silicon carbide, resulting in an exceptionally high upper critical magnetic field. This discovery not only establishes a new method for creating unconventional superconducting materials through interfacial engineering, but also promises exciting possibilities for developing advanced quantum and spintronic devices.

Van der Waals Heterostructures for Novel Devices

Van der Waals heterostructures, created by stacking two-dimensional materials, represent a revolutionary platform for materials design and device fabrication. These structures allow the combination of dissimilar materials with tailored electronic, optical, and mechanical properties, offering unprecedented control over material characteristics. Realising the full potential of these heterostructures requires a deep understanding of the interfacial phenomena that govern their behaviour, particularly the impact of interlayer coupling and charge transfer processes. Moiré patterns, arising from slight mismatches between the lattice constants of adjacent layers, significantly influence the electronic band structure and can lead to emergent phenomena such as superconductivity and correlated insulating states.

Despite substantial progress in fabricating and characterising van der Waals heterostructures, a comprehensive understanding of the interplay between Moiré potential, interlayer coupling, and charge distribution remains elusive. This research addresses this critical gap by developing a novel approach to directly map the interfacial charge distribution and interlayer potential in twisted van der Waals heterostructures with atomic-scale precision. The primary objective of this work is to establish a robust methodology for characterising the interfacial electronic structure of twisted van der Waals heterostructures. This involves combining scanning tunnelling microscopy with first-principles calculations to correlate observed spatial variations in tunnelling current with the underlying atomic structure and electronic states. By quantitatively mapping the interfacial potential and charge density, the research aims to elucidate the mechanisms governing charge transfer and interlayer coupling in these systems. Ultimately, this improved understanding will facilitate the rational design of van der Waals heterostructures with tailored properties for advanced electronic and optoelectronic devices.

Gallium Superconductivity via Heterostructure Engineering

Scientists engineered a novel heterostructure to investigate unconventional superconductivity, successfully synthesising trilayer gallium sandwiched between epitaxial graphene and a 6H-SiC(0001) substrate. This innovative approach utilises plasma-free, carbon buffer layer-assisted confinement epitaxy, enabling the creation of an air-stable material with tailored electronic properties. The method overcomes challenges associated with light-element superconductors by leveraging interfacial hybridization with the SiC substrate. The study pioneers a technique to induce Ising-type superconductivity in gallium, a material not traditionally considered a strong candidate.

Researchers meticulously controlled the growth process to create a confined gallium layer, fostering strong atomic orbital hybridization between the gallium and the SiC substrate. Electrical transport measurements demonstrate a superconducting temperature of approximately 3. 50 K and a remarkably high in-plane upper critical magnetic field, reaching 21. 98 T at 400 mK, significantly exceeding the Pauli paramagnetic limit of 6. 51 T.

To understand the underlying mechanisms, scientists employed angle-resolved photoemission spectroscopy (ARPES) in conjunction with theoretical calculations. ARPES measurements reveal a distinct pair of hole Fermi surfaces near the K and K’ valleys, aligning with predictions from the developed theoretical model. This detailed analysis confirms the presence of split Fermi surfaces and Ising-type spin textures within the confined gallium layer, providing crucial insights into the pairing symmetry and the origin of the enhanced superconducting properties. Incorporating finite relaxation time induced by impurity scattering into an Ising-type superconductivity model accurately reproduces the entire temperature-dependent upper critical magnetic field phase diagram.

Enhanced Superconductivity in Gallium Heterostructures

Scientists have successfully demonstrated unconventional superconductivity in a novel gallium-based heterostructure, achieving properties that significantly surpass those observed in bulk gallium materials. The team synthesised trilayer gallium confined between graphene and silicon carbide, creating an air-stable material exhibiting robust superconductivity due to unique interfacial effects. Electrical transport measurements reveal an exceptionally high in-plane upper critical magnetic field, reaching approximately 21. 98 Tesla at 400 millikelvin, which is 3. 38 times greater than the Pauli paramagnetic limit of 6.

51 Tesla. This remarkable enhancement stems from the interplay between quantum confinement and atomic orbital hybridization at the interface between the gallium layer and the silicon carbide substrate, inducing Ising-type superconductivity. Angle-resolved photoemission spectroscopy, combined with theoretical calculations, confirms the presence of split Fermi surfaces and distinct spin textures within the confined gallium layer. Incorporating impurity scattering into a model of Ising-type superconductivity accurately reproduces the entire temperature-dependent upper critical field phase diagram. The results demonstrate a superconducting coherence length of approximately 68.

6 nanometers and an extrapolated upper critical field reaching 27. 89 Tesla at zero Kelvin, exceeding the Pauli limit by a factor of 4. 28. Furthermore, the superconducting thickness is estimated to be 0. 60 nanometers, comparable to the physical thickness of the trilayer gallium. This innovative approach establishes a new strategy for realising unconventional pairing wavefunctions and opens exciting possibilities for developing scalable superconducting quantum electronic and spintronic devices through precise interfacial engineering. The carbon buffer layer-assisted growth technique prevents plasma-induced defects, preserving the structural integrity of the graphene and yielding an atomically flat gallium layer.

Gallium Confinement Yields Unconventional Superconductivity

This research demonstrates the creation of a novel superconducting material by confining gallium between layers of silicon carbide. The team successfully synthesised a trilayer gallium structure and observed superconductivity arising from the interaction between the gallium and the silicon carbide substrate. Electrical measurements reveal a significantly enhanced upper critical magnetic field, exceeding the predicted limit for conventional superconductivity, and temperature-dependent data align with a model incorporating Ising-type superconductivity. These findings establish a new approach to designing unconventional superconducting materials by combining quantum confinement with interfacial hybridization. The study highlights the potential for this method to create materials suitable for advanced quantum and spintronic devices through precise interfacial engineering. Future research directions could focus on exploring different material combinations and refining the understanding of the underlying mechanisms driving this enhanced superconductivity, potentially leading to the development of more robust and efficient superconducting technologies.